The present invention relates to a device that detects the wheel angle of an industrial vehicle such as a forklift. More particularly, the present invention pertains to a structure for installing a wheel angle detector at a predetermined position.
The body frame of a typical forklift is prevented from being excessively tilted with respect to the rear axle by centrifugal force generated during turning. Specifically, the tilting, or swing amount, of the rear axle is controlled during a turn of the vehicle based, for example, on the vehicle speed and the angle of the steered wheels. Japanese Examined Patent Publication No. 4-24270 discloses a method for detecting the angle of the steered wheels of a forklift.
The forklift disclosed in the publication includes a power steering apparatus. The power steering apparatus has a steering shaft, which is rotated by manipulation of a steering wheel, and a valve unit coupled to the steering shaft. The valve unit supplies hydraulic oil to and drains hydraulic oil from a cylinder in accordance with rotation of the steering shaft. The cylinder has a pair of piston rods protruding from its sides. Each piston rod is coupled to a vehicle wheel. Hydraulic oil from the valve unit moves the piston rods. Accordingly, the piston rods steer the wheels. The moving amount of the piston rods is detected by a stroke sensor. The angle of the wheels is computed based on the value detected by the stroke sensor.
In another method for detecting the angle of steered wheels, linear movement of piston rods in a cylinder is converted into rotation by a converter such as a link mechanism. This rotation is detected by a potentiometer. The angle of the steered wheels is detected based on the value detected by the potentiometer.
The first method, in which the movement of piston rods is detected by a stroke sensor, complicates the computation of the wheel angle. Moreover, since the stroke sensor is expensive, the first method is costly. In the latter method, where linear movement of piston rods is converted into rotation and is detected by a potentiometer, the potentiometer is relatively inexpensive and thus reduces the cost. However, this method requires a converter such as a link for converting movement of the piston rods to rotation. This increases the number of parts and complicates the installation of the apparatus. Further, if the converter is not assembled accurately, the detection of the wheel angle will be inaccurate.